Historically, valve lift profiles were fixed relative to the angular position of the engine crankshaft and the amount of lift imparted to each valve was also fixed. This adversely limited the performance and efficiency of internal combustion engines, and, in turn, had a negative impact on emissions. by having fixed lift profiles inherent compromises must be made between low and high speed operation, also necessitating the use of throttling devices in the internal combustion engine that introduce their own inefficiencies.
To combat these inefficiencies, modern internal combustion engines utilize several methods or devices to vary the valve lift profile to better manage the air flow into and out of the internal combustion engine cylinder. Among these are a group of devices intended to vary lift profiles by selectively switching between two or more different lift profiles as needed during operation. To date, this has been accomplished by the inclusion in a valvetrain of various devices, either alone or in unison with other devices, such as cam profile switching roller finger followers.
Such cam profile switching roller finger followers are known in the art and generally require relatively large envelope space with a related large mass moment of inertia. In a small and tightly packaged valvetrain, such space requirements add mass and are thus counter to providing higher performance and efficiency.
Typically, known roller finger followers have a high lift mode, a low lift mode and sometimes a no lift mode. They may comprise an outer elongated body, one end of which mates with a valve stem and operates on the valve stem, and a second end which is in contact with a hydraulic lash adjuster. An inner elongated body may be centrally located in the outer elongated body, housing a cam follower that is operated on by the earn so as to provide motion to the finger follower. The inner elongated body may have two modes, a locked mode and an unlocked mode. A latching or locking mechanism is incorporated into the roller finger follower assembly and is used to lock the inner elongated body in a stationary position. When the inner elongated body is locked in a stationary position, contact by the cam of the camshaft forces movement of the finger follower which translates into movement of the valve through the valve stem. When the locking pin or latch is released, the inner elongated body may move freely relative to the outer elongated body and no movement is translated to the valve of the engine. Typically, the inner elongated body pivots at one end, where it is attached to the outer elongated body, to move freely.
In order to maintain contact between the cam and the cam follower during the unlocked periods, a lost motion spring is employed. A typical lost motion spring is either helical or torsional.